1. Field of the Invention
The present invention relates to a method and device for triggering lung ventilatory support in response to myoelectrical activity of the diaphragm (or other inspiratory-related muscle), or in response to myoelectrical activity of the diaphragm (or other inspiratory-related muscle), inspiratory flow and/or inspiratory pressure in combination.
2. Brief Description of the Prior Art
Triggering of ventilatory support using airway inspiratory flow and/or pressure is affected by many factors including:
inspiratory muscle function, i.e. how activation is translated into tension, and how tension is translated into pressure; and
respiratory mechanics such as the elastic and resistive components of the respiratory system.
A drawback of the prior art airway inspiratory flow and/or pressure based ventilatory support triggering systems is that they cannot adequately detect inspiratory efforts in, for example, patients suffering from severe airflow limitation.
An object of the present invention is to use myoelectrical activity of the diaphragm or other respiratory-related muscles to trigger ventilatory support and/or to end the ventilatory support, in view of eliminating inspiratory flow and/or pressure trigger function related problems due to impedance of the ventilatory support system and the respiratory system. The present invention will also eliminate the problems related to leaks in the air flow system (infants).
Another object of the present invention is to provide a ventilatory support triggering method and device responsive to a combination of myoelectrical activity with inspiratory flow and/or pressure to guarantee adequate triggering of the ventilatory support apparatus in the eventual presence of delayed onset or absence of myoelectrical activity of the diaphragm or other respiratory-related muscle. The ventilatory support triggering method and device will improve detection of inspiratory efforts without jeopardizing the patient""s ability to use muscles other than the diaphragm to trigger the ventilatory support system.
A further object of the present invention is to provide a ventilatory support triggering method and device capable of triggering any ventilatory support system, and of triggering any mode of ventilatory support.
The present Invention relates to a method and device for triggering a ventilatory support apparatus in response to a respiratory effort via the use of myoelectrical activity of the diaphragm (or other muscles associated with respiratory effort) as well as a method and device for triggering a ventilatory support apparatus in response to a respiratory effort based on the combined use of myoelectrical activity of the diaphragm (or other muscles associated with respiratory effort) with respiratory flow and/or pressure.
More specifically, according to the present invention, there is provided a method for triggering ventilatory support from a ventilatory apparatus connected to a patient""s respiratory system to assist inspiration of the patient, comprising the steps of:
sensing myoelectrical activity of an respiratory-related muscle of the patient, to thereby detect respiratory effort of this patient;
producing a myoelectrical signal representative of the sensed muscle myoelectrical activity, and
triggering ventilatory support in relation to the myoelectrical signal to assist inspiration of the patient in response to respiratory effort of the patient.
In accordance with preferred embodiments:
the method for triggering ventilatory support further comprises the step of filtering from the myoelectrical signal at least one of the following disturbances: motion artifacts, ECG, electrical interference, and high frequency noise;
the triggering step comprises comparing an amplitude of the myoelectrical signal to a given threshold, and triggering ventilatory support when the amplitude of the myoelectrical signal is higher than the given threshold:
the triggering step comprises detecting an increment of an amplitude of the myoelectrical signal, and triggering ventilatory support in response to detection of this increment;
the method for triggering ventilatory support further comprises the steps of detecting decrement of an amplitude of the myoelectrical signal, and requesting non-triggering of the ventilatory support in response to that decrement;
the method for triggering ventilatory support comprises detecting the level of noise in the myoelectrical signal, and determining whether the respiratory-related muscle of the patient is active in relation to the detected level of noise; and
the sensing step comprises sensing myoelectrical activity of the respiratory-related muscle on two opposite sides of the center of a depolarizing region of this respiratory-related muscle, and the producing step comprises (a) generating two myoelectrical signal components in response to sensing of the myoelectrical activity of the respiratory-related muscle on the two opposite sides of the center of the depolarizing region, respectively, these two myoelectrical signal components having reversed polarities, (b) subtracting the two myoelectrical signal components from each other to produce a subtraction signal, (c) adding the two myoelectrical signal components to each other to produce an addition signal, (d) multiplying the addition signal by a predetermined constant to produce a multiplied signal, (e) comparing the multiplied signal to the subtraction signal, and (f) if the subtraction signal has an amplitude higher then an amplitude of the multiplied signal, accepting the subtraction signal as myoelectrical signal.
The present invention also relates to a method for triggering ventilatory support from a ventilatory apparatus connected to a patient""s respiratory system to assist inspiration of the patient, comprising the steps of:
sensing myoelectrical activity of an respiratory-related muscle of the patient to detect respiratory effort of the patient, and producing a myoelectrical signal representative of the sensed muscle myoelectrical activity;
measuring respiratory flow of the patient, and producing a respiratory flow signal;
measuring respiratory pressure of the patient, and producing a respiratory pressure signal; and
triggering ventilatory support in relation to the myoelectrical signal, respiratory flow signal and/or respiratory pressure signal to assist inspiration of the patient in response to respiratory effort of this patient.
Also in accordance with the present invention, there is provided a device for triggering ventilatory support from a ventilatory apparatus connected to a patient""s respiratory system to assist inspiration of said patient, comprising: sensor means for sensing myoelectrical activity of a respiratory-related muscle of the patient, to thereby detect respiratory effort of the patient; means for producing a myoelectrical signal representative of the sensed muscle myoelectrical activity; and means for triggering ventilatory support in relation to the myoelectrical signal to assist inspiration of the patient in response to respiratory effort of the patient.
According to a further aspect of the subject invention, there is provided a device for triggering ventilatory support from a ventilatory apparatus connected to a patient""s respiratory system to assist respiration of said patient, comprising a sensor for sensing myoelectrical activity of a respiratory-related muscle of the patient, to thereby detect respiratory effort of the patient, a signal processor for producing a myoelectrical signal representative of the sensed muscle myoelectrical activity, and a trigger circuit for triggering ventilatory support in relation to the myoelectrical signal to assist inspiration of the patient in response to respiratory effort of the patient.
Finally, the present invention relates to a device for triggering ventilatory support from a ventilatory apparatus connected to a patient""s respiratory system to assist respiration of the patient, comprising a myoelectrical activity sensor for sensing myoelectrical activity of a respiratory-related muscle of the patient to detect respiratory effort of the patient, and producing a myoelectrical signal representative of the sensed muscle myoelectrical activity, a respiratory flow detector for measuring respiratory flow of the patient, and producing a respiratory flow signal, a respiratory pressure detector for measuring respiratory pressure of the patient, and producing a respiratory pressure signal, and a logic trigger circuit for triggering ventilatory support in relation to the myoelectrical signal, respiratory flow signal and/or respiratory pressure signal to assist inspiration of the patient in response to respiratory effort of the patient.
For instance, the diaphragm electromyogram (EMG) represents the motor unit recruitment and firing rate and hence the inspiratory effort of the diaphragm which normally is the principal inspiratory muscle. Other muscles, for example parasternal intercostal muscles, sternocleidomatoids, scalenes, alae nasi, etc., associated with inspiratory efforts can also be useful sources for determining the onset of an inspiratory effort. The inspiratory flow and/or pressure also represent a source of global inspiratory effort, i.e. the inspiratory effort made by all chest wall muscles participating in the inspiration. The pressure can be replaced by direct measurements of transpulmonary, transabdominal or transadiaphragmatic pressures. An inspiratory effort can be first detected by the diaphragm EMG and an instant later as inspiratory flow and/or pressure. However, limitations of both methods to detect a breathing effort may occur depending on the condition of the patient. One limitation of using the diaphragm EMG is that under certain conditions, inspiratory muscles other than the diaphragm may initiate the inspiration, such that diaphragm EMG occurs later than inspiratory flow and/or pressure. One limitation of using airway inspiratory flow and/or pressure measurements is that under certain conditions, the inspiratory effort is not revealed by such measurements and consequently the ventilatory support apparatus is not triggered.
The use of EMG to trigger ventilatory support apparatuses requires extremely high quality of the EMG signal. Filtering and artifacts due to movements of the diaphragm with respect to the muscle must be minimized. Signal artifacts of nondiaphragmatic origin must be eliminated. An example of signal artifacts of non-diaphragmatic origin is ECG.
The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive description of a preferred embodiment thereof, given by way of example only with reference to the accompanying drawings.